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Solar flares: X-class (Yes, that's a real thing.)

Though it sounds suspiciously like a promo for 'X-Men: First Class,' an X-class solar flare is a massive solar storm capable of devastating satellite communication. On Friday, two X-class flares erupted from the sun's surface, the first X-class flares in five months.

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A-class flares are almost indistinguishable from background solar radiation, followed by B, C, M and X. Each letter represents a 10-fold increase in the solar flare's energy output, so an X is ten times an M and 100 times a C. An X2 is twice as strong as an X1. An X3 is three times as powerful as an X1, and so on.

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The most powerful solar flare ever measured occurred November 4, 2003, during the last solar maximum. It was so powerful that it blinded the sensors watching it, which max out at X17. Later calculations estimated that the flare reached a "whopping" X45.

A-, B-, and C-class flares are too weak to affect Earth in any meaningful way. M-class flares can cause brief radio blackouts at the poles, and are associated with radiation storms that might endanger astronauts. (Those of us on the surface of the Earth are protected from the radiation by Earth's magnetic field, which shields us from most incoming radiation.)

And then there are the X-class flares, which can be – by far – the largest explosions in the solar system. When the sun's magnetic fields cross over each other, loops dozens of times the size of Earth leap up off the sun's surface. The biggest flares can produce as much energy as a billion hydrogen bombs.

Fortunately for us, the sun emits energy in all directions, not just toward Earth, so most of the solar storm activity is blown out harmlessly into space. 

When the energy is directed at Earth, flares and coronal mass ejections (CMEs) can harm satellites, communications systems, and even ground-based technologies and power grids. 

NASA and NOAA aren't yet sure whether or not Friday's solar flares kicked off a CME, but they haven't seen any evidence of one yet. Even without a CME, X-class solar flares can disturb GPS signals and cell phone reception for as long as the flare lasts, which can be anywhere from minutes to hours.

Both of Friday's solar flares did cause radio blackouts, reported the Space Weather Prediction Center at a 2 p.m. update on Friday afternoon. 

"Our Earth is living in a star. We're living in the atmosphere of the sun," says Poland. "We're trying to study (solar flares and CMEs) like weather, and make predictions and monitor them just like we do weather on Earth, so that power companies and satellite operators and others will be prepared well in advance for anything that might happen." 

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